Field of the Invention
The present invention relates to a one-component developing apparatus for developing an electrostatic latent image with one-component toner.
The method of electrophotography disclosed in U.S. Pat. No. 2,297,791 to Carlson has a feature that "a photosensitive body having a photoconductive insulating layer is charged uniformly so as to form an electrostatic latent image by exposing an image, and the electrostatic latent image is visualized, that is, developed with a material such as electroscopic powder, and then transferred and fixed onto paper." Well known methods for developing an electrostatic latent image are the cascade developing process, the magnetic brush developing process, and the liquid developing process.
Another important developing method is transfer development which uses a toner carrier, called a donor, disclosed in U.S. Pat. No. 2,895,847. The transfer development described in this patent includes the cases of (1) a toner layer not in contact with a photosensitive body where the toner flies the gap between the toner layer and the photosensitive body, (2) a toner layer which contacts a photosensitive body while rotating, and (3) a toner layer which contacts a photosensitive body so as to slip on a picture portion. The transfer development is also known as the touchdown developing method.
FIG. 10 is a schematic diagram of a conventional magnetic one-component developing apparatus, which shows the case where the deflection angle .theta..sub.b of a plate spring is negative when a toner amount restricting member is urged onto a developer carrier. FIGS. 11(a) and 11(b) are side and perspective views illustrating the pressed-contacting state between the toner amount restricting member and the developer carrier. FIG. 12 is a schematic diagram illustrating the case where the deflection angle .theta..sub.b of the plate spring is positive in the developing apparatus of FIG. 10.
In the drawings, a developing apparatus is disposed close to a position opposite to an electrostatic latent image receiving member constituted by a photoconductive drum 1 which can hold an electro-static latent image 2 thereon. The developing apparatus is constituted by a hopper 3 for storing one-component magnetic toner 4, a magnet roll 5 having a plurality of magnetic poles of different polarities formed alternately, a non-magnetic cylindrical sleeve or developer carrier 6 supported so as to be rotatable around the magnet roll 5, and a toner amount restricting member 7. The magnet roll 5 is supported in the developer carrier 6 so as not to rotate. The toner amount restricting member 7 is urged onto the developer carrier 6 so as to restrict the amount of magnetic toner adhering on the developer carrier 6. The developer carrier 6 and the toner amount restricting member 7 are disposed within the hopper 3, and the developer carrier 6 is disposed close to the photoconductive drum 1 in the developing area.
In such a developing apparatus, the one-component magnetic toner 4 stored in the hopper 3 is held on the surface of the developer carrier 6 by the magnetic force of the magnet roll 5. The amount of the toner adhering on the developer carrier 6 is controlled to be 0.5 to 2.0 mg/cm.sup.2 by the toner amount restricting member 7 constituted by a plate spring 7a and a soft elastic member 7b. Then, by the revolution of the developer carrier 6, the toner on the developer carrier 6 is fed into a developing area in which the photoconductive drum 1 and the developer carrier 6 are opposite to each other. A DC-super-imposed AC voltage is being applied to the developer carrier 6 from an AC high voltage power supply 8 and a DC power supply 9, so that the electrostatic latent image 2 on the photoconductive drum 1 is developed with the magnetic toner in the developing area A. Examples of representative prior art references include Japanese Patent Unexamined Publication No. 54-51848, Japanese Utility Model Unexamined Publication No. 58-146249, U.S. Pat. Nos. 3,372,675 and 3,426,730.
On the other hand, FIG. 13 is a schematic diagram of a conventional one-component developing apparatus using non-magnetic toner showing the case where the deflection angle .theta..sub.b of a plate spring is negative when the toner amount restricting member is urged upon a developer carrier, and FIG. 14 is a schematic diagram illustrating the case where the deflection angle .theta..sub.b is positive in the one-component developing apparatus shown of FIG. 13 (reference is made to Japanese Patent Unexamined Publication No. 60-53975).
In this apparatus, a non-magnetic one-component developer 4 is stored in a hopper 3 so that the developer 4 is supplied to a developer carrier 10 by a feeding member 13 rotating in the direction the arrow at the same peripheral speed as that of the developer carrier 10. A toner amount restricting member 7 comprising a plate spring 7a and a soft elastic member 7b is provided in contact with the developer carrier 10 at predetermined pressure. The developer 4 supplied onto the developer carrier 10 is fed to the position of the toner amount restricting member 7 by the revolution of the developer carrier 10 so as to form a predetermined uniform thin layer of the developer 4. After being sufficiently charged, the uniform thin layer of developer 4 is fed to a position A opposite the electrostatic latent image receiving member 1. An AC voltage is applied to the developer carrier 10, so that the developer is caused to fly onto the electrostatic latent image receiving member 1 by an alternating electric field generated in the gap between the electrostatic latent image receiving member 1 and the developer carrier 10, so as to develop the electrostatic latent image.
In the foregoing one-component developing apparatus, in order to uniformly and stably obtain the amount of toner to be fed to the developing area A, that is, the amount of toner on the developer carrier 6 or 10, the pressure of the soft elastic member 7b of the toner amount restricting member 7 must be regulated to make the soft elastic member 7b be in uniform contact with the developer carrier 6 or 10 in the axial and circumferential directions.
In the conventional developing apparatus, however, there are problems as follows. For example, as shown in FIGS. 11(a) and 11(b), the toner amount restricting member 7 is provided with the soft elastic member 7b made of rubber material on the side thereof pressed against the developer carrier 6. However, since the soft elastic member 7b is cut down at the top end of the plate spring 7a, a very slight unevenness occurs in the pressure distribution in the axial and circumferential directions of the soft elastic member 7b to the developer carrier 6 so that the amount of toner formed on the developer carrier 6 becomes uneven. This happens even if the toner-layer restriction contributing factors of the parts constituting the developing apparatus (for example, the accuracy in the linearity and parallelism of the toner amount restricting member 7 relative to the developer carrier 6, the accuracy in way of support of the toner amount restricting member 7, the accuracy in unevenness of cramping the toner amount restricting member 7, and the like) are made severe.
If the contact-pressure of the toner amount restricting member 7 against the developer carrier 6 or 10 is set high enough to improve the unevenness of the pressure distribution, it becomes necessary to make the driving torque of the developer carrier 6 or 10 high, so that a high driving power is required. By the high driving power, deflection may be caused in the developer carrier 6 or 10, or the toner may be deteriorated by heat due to friction between the toner amount restricting member 7 and the developer carrier 6 or 10, so that it is impossible to maintain an even stable amount of toner adhering to the developer carrier 6 or 10 and thereby impossible to perform developing with high reliability.